The closest you get to negotiating is by doing something like, say you want to go for Christmas after joining, but it is all booked. Sometime the rep can find a room somehow, if you push for one. They are pretty good at doing this to make a sale.
Or you can negotiate for FPs and similar items. We did succeed in negotiating for a $1,000 gift card, as I recall this was because we named a few members that referred us, but can't remember all of the reasons, but then they offered to take that off the balance in lieu of giving the gift card.
We are not sure why that offer was made, but we certainly accepted it.
Also, because we were so close to the end of the use year, they gave us the previous use year points and offered to bank them for us, even though we would have been outside the banking window. We didn't take them up on that, as we wanted to use the points before the end of the use year anyway, but the offer was there.
These are the kinds of things you can negotiate, price is usually what they offer it to you at and cannot be negotiated.